Superconductors are more than 150 times more efficient at carrying
electricity than copper wires. However, to attain the superconducting state,
these materials have to be cooled below an extremely low, so-called transition
temperature, at which point normal electrical resistance disappears. Developing
superconductors with higher transition temperatures is one of physics' greatest
quests.

Until now, copper-laden materials called cuprates have been the only
superconductors whose transition temperatures are higher than the liquid
nitrogen boiling point at -321F (77 K). Whether researchers can make transition
temperatures higher in such materials remains a challenge.

Now, researchers at the Carnegie Institution's Geophysical Laboratory, with
colleagues, have unexpectedly found that the transition temperature can be
induced under two different intense pressures in a three-layered bismuth oxide
crystal referred to as "Bi2223." The higher pressure produces the
higher transition temperature. They believe this unusual two-step phenomena
comes from competition of electronic behavior in different kinds of
copper-oxygen layers in the crystal. The work is published in the August 19,
2010, issue of Nature.

"Bi2223 is like a layered cake," explained lead author Xiao-Jia Chen at
Carnegie. "On the top and bottom there are insulating bismuth-oxide layers. On
the inside of those, come layers of strontium oxide. Next, are layers of copper
oxide, then calcium, and finally the middle is another copper-oxide layer.
Interestingly, the outermost and inner layers of copper oxide have different
physical properties resulting in an imbalance of electric charge between the
layers."